Food and drink products and other perishable items are often packaged in tubular containers that are sealed at both ends. These tubular containers typically include at least one structural body ply and are formed by wrapping a continuous strip of body ply material around a mandrel of a desired shape to create a tubular structure. The body ply strip may be spirally wound around the mandrel or passed through a series of forming elements so as to be wrapped in a convolute shape around the mandrel. At the downstream end of the mandrel, the tube is cut into discrete lengths and is then fitted with end caps to form the container.
Tubular containers of this type typically include a liner ply on the inner surface of the paperboard body ply. The liner ply prevents liquids such as juice from leaking out of the container and also prevents liquids from entering the container and possibly contaminating the food product contained therein. Preferably, the liner ply is also resistant to the passage of gases, so as to prevent odors of the food product in the container from escaping and to prevent atmospheric air from entering the container and spoiling the food product. Thus, the liner ply provides barrier properties and the body ply provides structural properties.
Conventional liner plies most often include aluminum foil, which has good barrier properties and also has advantageous strength properties. In particular, the liner is wound onto the mandrel prior to the winding of the body ply and must be sufficiently strong and stiff to be independently wound on the mandrel without stretching or wrinkling. In addition, the aluminum foil layer typically includes a kraft paper backing for allowing the foil layer to be adhered to the paperboard body ply. Because of the support provided by the kraft-backed foil layer of the liner, such liners are known as "supported" liners.
Aqueous based adhesives (or "wet adhesives") are preferred for adhering the liner ply to the body ply because solvent-based adhesives have become disfavored in light of various environmental concerns over their use and disposal. However, it has heretofore been difficult to get the aqueous adhesives to stick to the smooth and impervious surface of the aluminum foil layer. Accordingly, a kraft paper backing has been preadhered to the foil layer so that the liner can be adhered to the paperboard body ply with wet adhesives. Kraft paper also adds additional cost and thickness to the liner.
Typically, a liner having a foil layer includes a polymeric layer on the surface of the foil that faces inward toward the interior of the resulting container. The polymeric layer prevents product in the container from coming into contact with the foil layer, which in some cases can cause a reaction that can corrode the foil and discolor or otherwise adulterate the product. The polymer layer may also improve the abrasion-resistance of the foil. The polymer layer frequently is also a heat-sealable material permitting one edge portion of the liner strip to be heat sealed to an overlying opposite edge portion of the strip.
In the manufacture of tubular composite containers, a strip of liner material is wrapped about a shaping mandrel and is advanced along the mandrel as the tubular composite container is formed. At the line speeds currently being used in the commercial manufacture of such containers, the liner strip is typically advanced at a linear rate of 400 feet per minute or more and is compressed upon the mandrel by the paperboard strips wrapped on top of the liner and by the belt or other device that advances the tubular container along the mandrel. Consequently, there is considerable friction between the mandrel and the liner, which generates heat. This heat can cause softening of the polymer layer of the liner that is in contact with the mandrel, with the result that the liner tends to adhere to the mandrel and is "scuffed" as it advances along the mandrel.
To help counteract this scuffing tendency, a lubricant is typically applied to the inner surface of the liner. Additionally, in some cases the mandrel is chilled so that the mandrel temperature is kept sufficiently low that the polymer layer of the liner is less prone to softening and sticking to the mandrel. However, where the polymer film layer performs the function of a heat seal layer, a dilemma of sorts is faced wherein a low mandrel temperature is desirable for reducing scuffing and sticking of the liner on the mandrel, while a higher mandrel temperature is desirable for facilitating the activation of the heat-sealable polymer layer to form a seal.
Where a supported liner is used, this dilemma can be largely avoided by heating the liner, or at least the edge portions that are overlapped to form a seal, to a temperature above the sealing temperature for the polymer layer just prior to wrapping the liner about the mandrel. The relatively large mass of the foil and kraft layers of the liner operates as a heat sink which holds the heat long enough that the liner edge portions can be heat sealed to each other when the liner strip is wrapped on the mandrel.
However, foils are expensive, and so it is desired to provide a container and a method of making such as container which includes an "unsupported" liner having the requisite barrier properties without the aluminum foil layer and kraft layer. When an unsupported liner is used, however, the heat sink function of the foil and kraft layers is eliminated. As a consequence, the relatively thin polymer film liner is difficult to heat because of its low mass which tends to dissipate heat rapidly.
The use of unsupported liners also presents other technical challenges. For example, because of the problems associated with winding an unsupported liner on the mandrel, such as stretching, creasing or other misshaping of the liner, it has not been economically or commercially feasible with conventional winding apparatus and methods to manufacture a container having an unsupported liner ply. Nevertheless, in view of the considerable material and cost savings that unsupported liners offer, it would be highly desirable to provide methods and apparatus for making tubular composite containers with unsupported liners.
Unsupported liners also offer advantages in addition to material and cost savings. More particularly, the elimination of the kraft layer enables straight overlap seams to be used in the liner, rather than the conventional "anaconda fold" seams traditionally used with kraft-backed liners. In an anaconda fold, the underlying edge of the liner ply is folded back on itself and adhered to the overlying edge. The anaconda fold allows the polymeric layers on the surface of the foil layer to be heat sealed together. Alternatively, a hot melt adhesive can be used to seal the underlying edge of the liner ply to the overlying edge. The edge of the kraft paper thus is not exposed to the interior of the container and thus liquids in the container will not be absorbed by the kraft paper. An example of such a fold is illustrated in U.S. Pat. No. 5,084,284 to McDilda, et al.
Anaconda folds are undesirable, however, because of their increased thickness. The thickness of an anaconda fold seam is equal to three thicknesses of the liner ply. Thus, with relatively thick supported liners, the anaconda fold presents a substantial thickness and poses difficulties when attempting to hermetically seal the ends of the tubular container. Specifically, the ends of the tube are often rolled outwardly after being cut so as to form a rolled circular bead or flange on one or both ends of the tube and then end caps or membranes are applied and usually sealed to the bead with an adhesive sealant, heat sealing, or other technique. However, in the area where the thick anaconda fold seam forms a portion of the edge surface, the end surface of the bead or flange can be substantially non-planar thus forming hill-like and/or valley-like irregularities. Accordingly, an extra amount of adhesive sealant or heat seal material is required in order to fill the discontinuities and hermetically seal the tubular container. The additional application of adhesive sealant or heat seal material is disadvantageous because of the extra sealant that must be used and the increased difficulty in removing the seal by the consumer due to the additional sealant. For example, where a membrane includes a heat seal layer, the entire heat seal layer must be made thicker, even though the increased thickness is actually needed only around the periphery of the membrane where it contacts the bead.
Because of the problems noted above with respect to supported liners, efforts have been made toward developing methods and apparatus for making tubular composite containers having unsupported liners in which the foil and kraft layers are eliminated from the liner. Additionally, there have been sought methods and apparatus for making composite containers having liners formed without anaconda fold seams.
A liner formed entirely of one or more relatively thin polymer layers would be particularly beneficial in that the additional foil and kraft layers would be eliminated along with their attendant costs, and the liner seam would present a relatively slight bump at the curled end of the container so that problems of hermetically sealing closures on the container ends would be substantially reduced. Accordingly, the assignee of the present application has striven toward developing practicable methods and apparatus for making containers with such unsupported film liners. For example, the assignee of the present application has developed methods and apparatus for making composite containers with unsupported liners made of polymer film and without anaconda folds, as disclosed in commonly owned U.S. patent application Ser. No. 08/796,912 entitled "Polymeric Liner Ply for Tubular Containers and Methods and Apparatus for Manufacturing Same" filed Feb. 6, 1997, and U.S. Pat. No. 5,829,669 entitled "Tubular Container and Methods and Apparatus for Manufacturing Same" issued Nov. 3, 1998, the entire disclosures of which are hereby incorporated herein by reference.
The '912 patent application and '669 patent disclose composite container-forming methods and apparatus wherein, according to one embodiment, a polymeric liner strip is adhesively joined to a paperboard body-forming strip prior to being wrapped about a shaping mandrel. By "prelaminating" the polymeric liner strip and paperboard strip together, the liner is effectively structurally supported by the paperboard strip so that it is relatively easily advanced to the mandrel without becoming excessively stretched or otherwise misshapen in the process. The polymeric liner strip is offset relative to the paperboard to which it is adhesively joined such that a marginal edge portion of the liner strip extends beyond one edge of the paperboard strip. The laminated paperboard/polymeric strip is wrapped about the mandrel so that the edges of the paperboard strip overlap each other and the marginal edge portions of the polymeric liner overlap each other. One of the marginal edge portions of the liner strip includes a non-aqueous adhesive layer that is heat activatable. Before and/or while the laminated paperboard/polymeric strip is wrapped about the mandrel, the non-aqueous adhesive layer on the marginal edge portion is heated to at least its activation temperature, and the overlapping edges are heat sealed together. Thus, the resulting composite container has a polymeric liner formed without anaconda fold seams.
However, the apparatus used to laminate the body and liner plies together before wrapping the plies onto the mandrel may not be the most advantageous in some applications. For instance, in some cases a separate set of nip rollers is needed to effect the lamination. Additionally, it will be appreciated that both the liner supply and body ply supply rolls must be located on the same side of the mandrel, which can make the placement of the supply rolls and the routing of the plies to the mandrel more complicated than would otherwise be the case if both the liner and body plies did not have to approach the mandrel from the same side. Replacement of the rolls may also be more difficult where the two supply rolls are located close together as they would tend to be in order to make efficient use of space.
In light of the foregoing, it would be highly desirable to provide methods and apparatus capable of making a composite container with an unsupported polymer film liner. Furthermore, it would be desirable to provide methods and apparatus permitting the formation of such a container without prelaminating the body and liner plies. It would also be desirable to provide methods and apparatus allowing either same-side or opposite-side winding of the body and liner plies onto the mandrel so as to increase the flexibility available to the designer and user of the apparatus in locating the body and liner supply rolls.